


We're Built on Sex

by NihilismPastry



Series: Laced and Bound [1]
Category: Undertale (Video Game)
Genre: After care, Animalistic Sans, BDSM, Bara Sans, Beast Tale AU, Beasttale AU, Dominate Sans, F/M, Female Reader, Knot kink, Lots of After care, Possessive Sans, Reader Is Not Frisk, Small reader, beasttale, human reader, more tags added as story continues, one shot series, part of a one-shot collection
Language: English
Status: Completed
Published: 2016-08-23
Updated: 2016-08-23
Packaged: 2018-08-10 11:38:54
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,688
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7843474
Author URL: https://archiveofourown.org/users/NihilismPastry/pseuds/NihilismPastry
Summary: <blockquote class="userstuff">
              <p>Sans fucks his mate in the shower, but they come to the conclusion that they know nothing about each other.</p>
            </blockquote>





	We're Built on Sex

**Author's Note:**

> Recently found this thing called Beast Tale, unsurprisingly I loved it, so here's a fic about it. Um, here's a link to the creator's tumblr. http://get-rammed.tumblr.com/

There was something about watching his mate bathe that made his protective instincts flair. Without any of her clothes, her boundaries and guards let down, and her mind at ease thanks to a locked door was almost preposterous. You'd think after six months living with him, she would have figured out that locked doors meant little to monsters. They were larger, stronger, and faster than any human. The only advantage she had was her soul, and even that could be considered a bit of a stretch against a strong enough monster. Even the budding magic thanks to their teather wasn't refined enough to do any real damage against anyone.

He silently slipped off his clothes and let them drop to the floor. His phalanges brushed the clear shower curtain to the side, and his mate barely reacted. Her brown eyes fixed on him with a soft smile as he stepped into the shower behind her. "Ya knew I was here, didn't ya?"

"Mhm." She craned her neck back to look at him properly. "I heard you growling when you first came in." Her lips pursed a bit, as a thought came to her. "Actually, you always do that when you find me in the shower."

His phalanges dragged down her back. Her skin jumped from the feeling, but she didn't seem to complain. "Ya drive me crazy, ya know that?" He leaned down and licked her neck. She tasted like chemicals and raspberries, probably had something to do with her soap. "Ya act like no one can hurt ya." A soft moan escaped her lips when his teeth dragged over her throat. Beeds of blood welled from the wounds and slid down her skin in tantalizing rivelets. This only served to spurn him on. "That they don't want to split your teather with me." 

"Sorry, Sans, but I kinda like showering." She moaned when he pinched her ass. "I can't do that once a week crap that you and Papyrus do."

His mate was an utter chore. She needed as much upkeep as a pet, and talked back more often than one. Clearly she was used to him though, because three months ago she wouldn't have dared to act so bold. "Someone's forgetting who she belongs to, huh?" He licked from her jaw all the way up to her ear. "Press your hands against the wall, spread your legs, and stick that ass out."

"Sans-" She yelped when his hand smacked her ass. It left a nice red print that'd probably bruise later. "Yes, master."

"Then get to it."

She pressed her hands against the slippery tile, spread her legs, and presented her ass to him. His phalanges on one hand traced her spine, while the other fingers spread her vaginal lips. Seeing her wet like this without having done much made him want to plow into her. "Ya got no idea what you do to me." 

Going from her spine down her ass, his fingers finally teased at her entrance. The soft moan went up a pitch, and her thighs trembled. She wanted him inside her. That thought wrapped around his soul like a cobra and squeezed. Magic crackled and spasmed in the air, making a surge of heat curl through his bones.

He removed his fingers from her cunt and roughly grabbed a boob. "Ya ready, baby girl?" He lined his dick up and teased her slit. "Ya want me t'fuck ya into the wall?" His mate nodded, and Sans wondered if she really wanted this. He leaned down and bit an erogenous zone on her neck. This time it was hard, blood gushed from the wound and his mate screamed in both pain and pleasure. Sans let his tongue escape his mouth and lap at the diluted blood. Maybe fucking in the shower wasn't the best idea? "Come on slut, use your words. That mouth ain't just for sucking me off."

Her breathing was labored, and he knew she was hurting, but she spoke anyway. "F-fuck me."

He slid his dick a few inches into her warm cunt with. growl, but didn't hilt into her, she hadn't earned that right yet. "Come on, magic words."

"Please, fuck me already, dammit!"

"As ya wish, ya dirty whore."

He slammed his dick to the hilt, earning a deep growl from him and a sharp squeal from her. No matter how many times he fucked her, pushed her to her limits, she was still tight. His mate claimed it was some type of exercise she did, but Sans didn't particularly believe that. He had enough girth to stretch the fuck, heh, out of her. And they usually went at it like rabbits in heat, there should be no way she was as tight as she was. He guessed it was some type of magic she had dug up from her teacher.

He continued at a hard pace, his hands griping her chest, and his mouth on her neck. His tongue dug into her wound, and every time he did that she would writhe under him with a loud moan. Her fingers curled and her head bowed, under his hands he could feel her heart beating hard against her ribs.  _He_ was the one doing this to her.  _He_ was the one who got to see this side to her. No one else would be able to, not if he got a say in it. She was  _his_ mate, and he'd be damned if anyone even thought of you in this way. A low growl ripped through him, and he released his manhandle on her tit to grab her waist. He yanked her back, earning a weak squeal of surprise on her end, and thrust up into her. Her hands reached up and weakly curled into his ribs, making magic curl and spark in his bones. 

"Dammit you're so fuckin' soft." His free hand went straight to her boob again. He was a proud titty monster, but his mate's were the perfect size for him to grab."And you're warm too, ain't a cold part on ya." She garbled out a response, but he couldn't understand her. Huh, she was close already. "You wanna cum, don't ya? Ya wanna cum for me baby girl?"

She nodded erratically, her hair clinging to her face and his ribs. "Please let me cum!"

"Heh, guess ya figured it out the first time am I right?" He brought a hand up and choked her. There was just enough pressure to know he was there, but light enough she wouldn't break. "Go'head baby girl, cum for me."

Her already tight muscles clamped down on him as her spine arched. Her mouth opened wide and a stifled scream tried to escape her lips. He kept up his pace though, he was getting close now. Dammit, he loved seeing her face when she came. Some sense of pride in his wonderfully fucked up life surfaced, as did his possessive streak. He gripped her a bit harder as his thrusts become erratic and sloppy. She was _his_. This was _his_ mate. No one else could treat her this way. He leaned down and burried his nasal bone into her shoulder, causing the jagged piece to dig into her skin and make her bleed even more. "You're _mine_. Body, mind, and fucking soul." 

He pumped himself inside her a few more times, his magic begging to be realesed into her body. Once he hilted himself ,and his knot, he let go with a growl of what might have been her name. He leaned on the back wall and let go of her throat, his other arm secure around her waist so she wouldn't hurt herself while tied to him. "Ya alright?" 

A weak giggle escaped her and she craned her head back to look at him. "Fine, my throat just hurts." Another spurt of cum shot into her, making her moan. "I-I'll need some tea and a bath, cause this one's a bust."

"Ya were ripe for the taking, breast believe I was going't fuck your brains out."

She rolled her eyes, but a smile was still spread over her lips. 

* * *

 

It took a good half hour, but he finally managed to pull out of her. He wiped away the cum, occasionally licking some away, which earned him a second orgasm face to admire.  Once that was finished he bundled her up in her towel and set her on the counter, before turning the shower off. She wouldn't be able to get a bath for another hour or so, the hot water was gone. He turned the knobs on the shower to shut it off, before throwing on a pair of basketball shorts. He then picked his mate up and went downstairs. Papyrus wasn't home, apparently his 'kitten' was sick and he was determined to make her better, so he didn't worry about his own mate's state of undress. 

He went to the kitchen and set her on the counter. Once he was sure she wouldn't fall over, he grabbed a bottle of antiseptic from the top shelf and some cotton swabs. As much as he loved to bite the fuck out of her, he also knew that she was delicate. His bites were deep and if he didn't give them an initial clean she'd get sick. Plus, he learned that the scars looked better if they were cleaned. He pressed the cotton to the bottle and let it get soaked before holding up three fingers to her mouth. "Ya know the drill, suck."

She did as she was ordered, her tongue tentatively reaching out, before his fingers were encased in her hot warmth up to the knuckle. If she needed to she could bite down, it wouldn't kill him. He pressed the cotton to her neck, causing her to suck harder on her fingers and close her eyes. She never cried during this part, never screamed. She just tried to swallow his fingers as he whispered praises in her ear, while cleaning up the wound. Once he was finished he removed his spit covered fingers from her mouth, and tossed the cotton ball away. The wound on her shoulder didn't justify a cleaning, not to Sans anyway. It was barely a cut and was already starting to scab over. Not an obvious bite mark, but just a jagged mark that wasn't nearly as impressive.

With that done he grabbed a bright pink mug and a box of honey chamomile tea off the shelf he got the health supplies from. He filled the mug with water and put it in the microwave for a few seconds. 

"You know, it's a little weird." Sans glanced over to her, but didn't respond. "You're super dominate and do so many things to me, but you always make sure I'm better afterwards. I'm not sure if it's because Toriel and the arch-mage teathered us, or it's your natural personality."

The microwave dinged, and Sans took out the mug and set it on the counter next to her, before grabbing the box and putting a tea bag into the hot water. "It's both."

"Huh?"

"If I fucked ya for fun I wouldn't've even bothered with all this." He said as he grabbed a bottle of honey down from the shelf. "But leaving a mate all beat up without looking after them ain't normal for any monster. Kinda like an instinct or something like that." He squeezed the bottle of honey and a gratuitous amount plopped into the mug, his mate pushed his arm away once she was satisfied. "So, it's both."

She picked up the mug and looked into it for a moment before taking a sip. He watched her throat flex as she drank the now luke warm tea, he could never understand how that didn't hurt. After a few moments she set the mug down again, and he grabbed a jar off the shelf and handed it to her. She didn't let him open already open jars anymore, not after the 'mayo conspiracy'. She grabbed a handful of jellybeans and popped them into her mouth. "Are you completely ruled by your instincts?"

"Why're you so curious?"

She swallowed her sweet treat and shrugged. "I guess the last few months have either been us being freaked out by each other, fucking, or trying to get my magic to work." She dug her hand back into the jar, moving her fingers to flick the yellow jelly beans out of the way. "I just want to know you a little better."

He stared at her for a few moments. It was true that they knew almost nothing about each other. In fact, the most he knew about her had everything to do with her after care kit and what she liked during sex. Considering she was now his mate, forcefully or not, it wouldn't hurt if he got to know her better. It'd probably do some miracles for his sanity. "Let's get ya in the bath, don't wanna get cum on the floors."

She set the jar on the counter and allowed him to pick her up. She tucked her head under his chin, a rueful smile on her lips. "That sounds kinda hot though. You cum inside me so much, I bet I could make it happen."

A low growl reverberated through his chest and his grip on her tightened. "That bath is'bout to become pretty fucking useless again."

She giggled, but didn't push him, a clear sign she was tired. He kicked open the bathroom door and set her on the toilet while he started the bath. He didn't like it when she used a lot of chemicals on her skin, so he never threw in bubble bath. However he did light the candles on the counter. The overly sweet smell of cotton candy flooded his senses. He watched his mate kick her feet as he set one of the blue candles down. "Sans, what's your favorite color?"

"Blue." He snorted at her unsurprised look. "And ya like pink, right?"

"How'd you know?"

He reached up and brushed a hand through her curls. "Ya fucked your hair up with the stuff, and it's all over your room."

"It's only a fourth of my hair, you make it sound like I did my whole head." She hummed when he began to scratch her head. "Uh, now you. Ask me a question."

He kept an eye on the tub as he thought about it. His mate didn't present herself as a hardcore mystery. Her emotions were always on display for anyone to see, and she didn't keep secrets. She was like a house with the windows open and very little furniture to clutter the space. In that regard she was so different from him, and that almost scared him. That type of openness could get you hurt in this world, yet she didn't seem to realize it, or if she did she just didn't care. Maybe that was what he should ask: 'Why in the hell are you so honest?'. But then he was likely to get a question that he didn't particularly want to answer either.

So, as he bent down to turn off the water he asked. "Why'd ya fuck up your hair?"

"Dye." She corrected. "And I did it on a dare in twelfth grade. It kinda stuck after that, and really helps to make me look a little cooler since my job requires looking like a badass straight out of hell." He took the towel off of her and set her into the water. She moaned and sunk deep into it, eyes shut in contentment. "Did you ever have a mate before me?"

His magic flared in his bones. "Nah, couldn't be bothered."

"Then are you mad that I'm your mate?" She was looking at him now, those brown eyes were trying to see through to his soul.

He put on his signature smirk and leaned back against the toilet. "That's two questions baby girl." She opened her mouth, but he cut her off. "Now, why do ya hate ketchup?"

**Author's Note:**

> So as you can see there's more going on then in the background than what's being shown. Personally, I love reading a story with an established relationship and action already happening. There will be flashbacks, so you'll know what happens eventually. Since this is all from Sans's view point, reader is never called 'You', always 'her' or a pet name. Oh, and if you have a request for a sex scenario or kink, then let me know so I can add it.


End file.
